Theorem al0ssb 5235

Description: The empty set is the unique class which is a subclass of any set. (Contributed by AV, 24-Aug-2022.)

Assertion

Ref	Expression
al0ssb	⊢ (∀𝑦 𝑋 ⊆ 𝑦 ↔ 𝑋 = ∅)

Distinct variable group:   𝑦,𝑋

Proof of Theorem al0ssb

Step	Hyp	Ref	Expression
1		0ex 5234	. . 3 ⊢ ∅ ∈ V
2		sseq2 3951	. . . 4 ⊢ (𝑦 = ∅ → (𝑋 ⊆ 𝑦 ↔ 𝑋 ⊆ ∅))
3		ss0b 4336	. . . 4 ⊢ (𝑋 ⊆ ∅ ↔ 𝑋 = ∅)
4	2, 3	bitrdi 286	. . 3 ⊢ (𝑦 = ∅ → (𝑋 ⊆ 𝑦 ↔ 𝑋 = ∅))
5	1, 4	spcv 3542	. 2 ⊢ (∀𝑦 𝑋 ⊆ 𝑦 → 𝑋 = ∅)
6		0ss 4335	. . . 4 ⊢ ∅ ⊆ 𝑦
7	6	ax-gen 1801	. . 3 ⊢ ∀𝑦∅ ⊆ 𝑦
8		sseq1 3950	. . . 4 ⊢ (𝑋 = ∅ → (𝑋 ⊆ 𝑦 ↔ ∅ ⊆ 𝑦))
9	8	albidv 1926	. . 3 ⊢ (𝑋 = ∅ → (∀𝑦 𝑋 ⊆ 𝑦 ↔ ∀𝑦∅ ⊆ 𝑦))
10	7, 9	mpbiri 257	. 2 ⊢ (𝑋 = ∅ → ∀𝑦 𝑋 ⊆ 𝑦)
11	5, 10	impbii 208	1 ⊢ (∀𝑦 𝑋 ⊆ 𝑦 ↔ 𝑋 = ∅)

Syntax hints:   ↔ wb 205  ∀wal 1539   = wceq 1541   ⊆ wss 3891  ∅c0 4261

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1801  ax-4 1815  ax-5 1916  ax-6 1974  ax-7 2014  ax-8 2111  ax-9 2119  ax-ext 2710  ax-nul 5233

This theorem depends on definitions:  df-bi 206  df-an 396  df-tru 1544  df-fal 1554  df-ex 1786  df-sb 2071  df-clab 2717  df-cleq 2731  df-clel 2817  df-v 3432  df-dif 3894  df-in 3898  df-ss 3908  df-nul 4262

This theorem is referenced by:  iota0def  44483  aiota0def  44539